1. Field
Disclosed herein is a lacquer composition, particularly an adhesive and corrosion-protective lacquer for rare earth permanent magnets, based on an epoxy resin mixture, a setting accelerator, a silane-based epoxy functional adhesion promoter and a solvent or a solvent mixture and to a method of manufacturing magnet systems using the aforementioned lacquer composition.
2. Description of Related Art
Magnets and magnet systems, particularly those which include neodymium-iron-boron magnets, must generally be protected from corrosion. This necessitates an appropriate coating, e.g. a lacquer coating.
When assembling magnet systems, magnets are furthermore connected adhesively beneath one another or to other workpieces, such as steel flux guides or other soft magnetic workpieces. It is thus required of the adhesive connection that it has a high strength, preferably >10 N/mm2 in conjunction with a high temperature resistance because, when used in motors, temperatures of up to 180° C. occur and high opposing fields act on the magnets. The adhesive connection must withstand these conditions.
In the case of so-called segmented magnet systems, which are composed of a plurality of individual magnets, the adhesive connection has the purpose of fixing the packet or holding it together and also being responsible for insulation of the individual magnets with respect to one another. Such systems are used, for instance, in large, electrically operating machines, such as ships motors, wind turbine generators, etc. The electrical insulation of the individual magnets prevents the occurrence of high eddy currents and thus overheating of the motor.
In the conventional manufacture of magnet systems, the magnets are commonly glued together with the aid of liquid high-performance adhesives (epoxy resins, acrylates etc.). The magnet systems are then provided with a corrosion-protective lacquer, generally a stoving varnish, which protects the system from environmental and chemical influences, depending on its usage. There is the problem in this case that lacquer voids occur, particularly in the vicinity of the adhesion gap as a result of trapped gas or air bubbles. Attempts were therefore made to apply the corrosion protection before or during the adhesion process.
DE 10 2006 012 839 B4 describes a lacquer composition based on an epoxy resin mixture, a setting accelerator, a silane-based epoxy functional adhesion promoter and a solvent, which has not only adhesive but also corrosion-protective properties so that when it is used the adhesion and the corrosion protection of the magnets can be effected in one method step. Magnets are coated in the method with the appropriate lacquer compositions and then fixed in position with the aid of spring or clamping devices in the arrangement of the subsequent magnet system. The magnet systems thus arranged are then brought together with the clamping tools up to the curing temperature in the furnace. The joint surfaces are brought into contact by the application of pressure with the aid of the spring tools, whereby the lacquer, which is preferably applied on both sides, flows together and simultaneously sets. The individual magnets are stuck together in this manner to form magnet systems. This method has the disadvantage that the individual components of the magnet system are only firmly stuck together at relatively high temperatures so that a complex tool technology with a corresponding application of pressure is necessary for firing the corrosion-protective lacquer in order to produce a magnet system with a sufficient strength.